Electron beam deflection circuits



Aug. 29, 1939. G. B. BANKS 2,370,847

I ELECTRON BEAM DEFLECTION cmcurrs Filed June 3, 1936 ATTORNEY PatentedAug. 29, 1939 UE'E'ED STAT.

George Baldwin Banks,

Chelmsford, England, as-

signor to Radio Corporation of America, a corporation of DelawareApplication June 3, 1936, Serial No. 83,196 In Great Britain June 8,1935 4 Claims.

This invention relates to cathode ray tube apparatus and moreparticularly to such cathode ray tube oscillograph arrangements of thekind wherein a cathode ray beam is deflected in at least one directionby electromagnetic deflection means. Though not limited to itsapplication thereto the invention is particularly Well adapted tocathode ray tube oscillograph apparatus for use for television and liketransmission or reception.

It is common in cathode ray tube television apparatus to cause an areato be explored or scanned by a cathode ray beam which sweeps across saidarea in a succession of lines and it is also common to produce thenecessary deflection for scanning action by means of electromagneticdeflecting coils acting on the cathode ray beam. Sometimes bothco-ordinates of scanning movement are obtained by deflecting coils andsometimes one only of the co-ordinate components is so obtained, but inany case the usual requirements for each component of scanningdeflection is that said component shall follow a substantiallyrectilinear saw-tooth wave form; that is to say each component ofscanning shall be such that the cathode ray beam is deflected in theappropriate direction at a constant speed and is then deflected back ata much higher constant speed. Now the obtaining of such a component ofscanning by means of electromagnetic deflecting means is a matter ofconsiderable difliculty in practice principally by reason of thenecessarily relatively high inductance of the deflecting coils. Therequirement is that the current wave form through the deflecting coilsshall be of substantially rectilinear saw-tooth wave shape but, owing tothe inductance of the said inflecting coils, the production of such acurrent wave devolves the application to the coils of a voltage waveform which rises from an initial value rectilinearly to a maximum valueand then comes down very sharply to a value well below said initialvalue thereafter rising very sharply back to said initial value. Thedownward peak in this wave form is necessitated by the inductance of thedeflecting coils.

The object of the present invention is to meet the difficulty abovereferred toand enable the deleterious efiect of the self-inductance ofde- 'flecting coils in a cathode ray tube to be substantiallyeliminated, or at any rate, very greatly reduced.

For the purpose of convenience in description that portion of thedeflecting wave form during which the deflection increases at asubstantially constant speed in one direction will be. herein referredto as the deflecting period and the successive portion during whichrapid return of the ray is effected will be herein referred to as thereturn period.

According to this invention in a cathode ray tube apparatus whereinelectromagneticdeflection in at least one direction is resorted to,means are provided for short circuiting or substantially short circuitduring return periods the deflecting coils employed for such deflection.

Preferably the short circuiting action is obtained by means ofelectronic or ionic discharge means connected across the deflectingcoils to be short circuited.

The invention is illustrated in the accompanying drawing in which Figs.1 and 2 show diagrammatically two embodiments thereof.

Referring to Figure 1 a neon or other gas-filled discharge device I isconnected across the deflecting coils 2 of a cathode ray tube apparatus(not shown), the said deflecting coils being energized in any convenientknown manner with a suitable voltage wave form. In the arrangement ofFigure l the voltage wave form is applied from a saw-tooth wavegenerator (not shown) between control grid 3 and cathode 4 of a valve 5Whose anode circuit contains a choke 6. The voltages set up across thechoke B are applied through condenser l to the deflecting coils 2. Theneon or other discharge device I is chosen. to have a break down voltagewhich is higher than the voltage which is set up across the coils 2during the deflecting period, but is less than the voltage which would(but for the provision of the discharge device) be set up across thesaid coils during the return period. It will be appreciated that owingto the fact that the return period is much shorter than the deflectingperiod, the voltage set up across the coils 2 due to theirself-inductance (i. e. the back E. M. F.) will be considerably higherthan the voltage set up across the said coils during the deflectingperiods and accordingly the gas discharge device I will flash onlyduring return periods (thereby effectively short circuiting the coils)but not during deflecting periods.

In the embodiment shown in Figure 2 the coils 2 are shunted by theanode-cathode space 89 of a gasfilled triode or gas relay II] the grid Hof which is connected to the cathode 9 through a suitable resistance I2in series with a negative bias source l3. By adjusting the bias on thegrid II the break-down voltage of the gas relay I!) may be adjusted. Oneadvantage of this em- 55 flection in mutually perpendicular directionsis resorted to short circuiting means may be associated with each of thetwo mutually perpendicu lar deflecting means. It will, however, beappreciated that the advantages of the invention are most marked inrespect of the high speed component of scanning deflection. v Incarrying out the invention as applied to the normal television caseusing electromagnetic deflection in both directions, it is accordinglynecessary merely to arrange for periodic short circuiting of thedeflecting coils which efiect scanning deflection in the line directionfor it is, of course, as regards the high speed component of scanningdeflection that the question of self-inductance of deflecting coils ismost material. If desired, however, means may be provided forperiodically short circuiting the coils for framing deflection also.

What I claim is:

1. In apparatus for controlling the deflection of an electronic beam, athermionic amplifying tube having anode, cathode and at least onecontrol electrode, means for impressing on a control electrode of saidtube an electrical impulse of predetermined wave form, inductivedeflecting means connected in the anode-cathode circuit of said tube, athermionic tube having anode, cathode, and at least one controlelectrode, means for connecting the said deflecting means in theanode-cathode circuit of said latter tube, and means for impressing on'a control grid of said latter tube an electrical impulse ofpredetermined wave form.

2-. An'apparatus for deflecting an electronic beam comprising a firstthermionic tube having anode, cathode and at least one controlelectrode, means for impressing on a control electrode of said tube anelectrical impulse of predetermined wave form, inductive deflectingmeans connected in the anode-cathode circuit of said tube, a secondthermionic tube having anode, cathode and at least one controlelectrode, means for connecting said inductive deflecting means in theanodecathode circuit of said second tube, means for adjustably biasingthe grid of said latter tube with respect to the cathode thereof, andmeans for impressing on a control grid of said latter tube an electricalimpulse of predetermined wave form.

.3. Apparatus in accordance with claim 2 wherein the electrical impulsesof predetermined wave form, impressed on the control grid of the firstand second tubes comprise waves of the same wave form.

4. Apparatus in accordance with claim 2 wherein the electrical impulsesof predetermined wave form'impressed on a control grid of the first andsecond tube comprise at least a portion of the same wave. 7

' GEORGE BALDWIN BANKS.

